Vapour-phase (p, ρ, T, x) behaviour and virial coefficients for the (ethane + carbon dioxide) system

Abstract

Accurate density measurements on three binary (ethane + carbon dioxide) mixtures with ethane mole fractions of 0.05023, 0.20031, and 0.49954 were carried out at temperatures from T = (273.15 to 323.15) K with pressures up to the dew-point pressure or 6.0 MPa, whichever was lower. The gas mixtures were prepared gravimetrically and a well-proven two-sinker magnetic suspension densimeter was utilized for the measurements. It was observed that sorption effects have an impact on the reproducibility of the density measurements of up to 0.04%. Considering all measurement uncertainties in temperature, pressure, density, and composition, the relative combined expanded uncertainty (k = 2) in density was estimated to be less than or equal to 3.8 × 10−4. Relative deviations of the experimental densities from the GERG-2008 equation of state were less than 0.5%, which is clearly within the uncertainty of this equation. Values and uncertainties of the second and third virial coefficients were calculated by correlating the isothermal experimental data to a third-order virial equation. Second interaction virial coefficients were determined as well, and excellent agreement with literature was obtained. The new experimental data presented in this work can be especially used to further improve the performance of multi-parameter equations of state for mixtures, particularly in the vicinity of the dew line.